In general, industrial furnaces are classified into various types according to products produced by the furnaces.
For example, the furnace types include an industrial incinerator for incinerating wastes, a melting furnace for iron mills for melting metal, a gas furnace for melting glass, a cement furnace, a pottery furnace and a calcining furnace.
One of operators' common demands relating to various furnaces is to frequently observe the inside of a furnace during the operation of the furnace using clear images.
Once a furnace is operated, the furnace is continuously operated for a certain period of time as long as a particular breakdown does not occur. Accordingly, the inside of the furnace should be inspected by frequently observing the inside of the furnace during the operation of the furnace.
A conventional method of observing the inside of an industrial furnace is generally implemented by forming a hole having a certain size through the wall of the furnace, placing a door in front of the hole to be selectively opened and closed, and observing the inside of the furnace through the hole using the naked eye with the door being opened.
Such a conventional method is used in about 70% of furnaces. In order to protect the eye and intercept strong visible rays when observing the inside of a furnace by the above-described method, a user should use an additional face protector to which an infrared glass is attached.
However, the conventional method is disadvantageous in that the thermal efficiency of a furnace is reduced due to the forming of a hole through the wall of the furnace, combustion mixture ratio can be changed due to the inflow of outside air, a viewing angle for observing the inside of the furnace with the naked eye is restricted due to a small-sized and long hole in the wall of the furnace, and an operator may be burned.
In order to solve the above problems, there was proposed another conventional method of monitoring the inside of a furnace by forming a hole through the wall of the furnace, forming a window using quartz or heat-resistant glass, placing a camera and a camera protective housing outside the window, and photographing images formed on the window using the camera and lenses.
However, this conventional method has a limitation in the monitoring of the inside of a furnace because only limited images obtained through the hole formed through the wall of the furnace can be observed.
Additionally, the glass is strongly resistant to heat, but weak to impact, abrasion and corrosion. As time passes, dirt, such as soot generated by combustion in the inside of a furnace, adheres to the inside surface of the window, so the transparency of the window is deteriorated and clear images cannot be obtained, thus the window requiring continuous maintenance.
This conventional method is more advantageous than the first conventional method, but is not appropriate for a large-sized furnace, and a furnace's temperature must be controlled precisely.
There was proposed still another conventional method of inserting an image device called a lens tube into the inside of the furnace and observing the inside of a furnace through a monitor.
In accordance with this conventional method, lenses are arranged in a conventional lens tube 1 in a row, a camera protective housing 3 is connected to the back of the lens tube 1, and a general camera is disposed in the camera protective housing.
As illustrated in FIG. 1, the housing 4 is mounted on a cylinder rail 7 with a housing support 6 attached to the cylinder rail 8. The lens tube 1 is inserted into a furnace by supplying compressed air through the compressed air supply valve 25 to the cylinder rail and therefore moving the housing support 6 so as to photograph and monitor the inside of the furnace. In the case of an abnormal situation, such as a checkup, a power failure or the interruption of compressed air, the lens tube 1 is retracted from the furnace by supplying compressed air to the compressed air supply valve 25 disposed on the front portion of the cylinder rail so as to protect the lens tube 1 from high temperature heat inside the furnace.
The image of the inside of the furnace is passed through lenses arranged in the lens tube 1 in a row, and transmitted in and formed in the image sensor disposed in the camera protective housing 3. Thereafter, the image is passed through the electric control box 30 and displayed on a control center monitor 100, so the monitoring of the inside of the furnace is enabled.
In this case, since the inside of the furnace has a high temperature, specially fabricated camera protective housing 3 and the lens tube 1 are cooled by compressed air supplied from the air control box 31 to protect them. Thereafter, the supplied compressed air is discharged to the outside along a certain path.
However, since the system for monitoring the inside of the furnace described above employs the cylinder type retraction device and the camera protective housing 4, and therefore additional structures are required to fixedly attach them to the system, the system becomes large, power is required and so causes breakdown, and maintaining and purchasing costs are high.